| 摘要 |
<p>A downhole tool (10) comprises a body (12) defining a bore. The body includes a valve arrangement (18) including flow ports (24) in the wall of the body. The ports may be opened or closed. In addition, a variable flow restriction (30) is provided in the bore (14), the degree of restriction tending to decrease as flow across the restriction increases. The variable flow restriction may be utilised to actuate the valve arrangement.</p> |
